Update the way how to remove environment variables for Jupyter ntb

This change slightly simplifies the way how the variables are removed
from the Jupyter spawner page for the notebook - now it doesn't depend
on particular variable values, but simply clicks until the remove button
is present on the page.

Another change here is that this variable removal is now run also in
case that the given set of variables to the `Spawn Notebook With
Arguments` keyword is empty. This will assure that any eventual
leftovers from previous test are cleaned up properly not affecting this
current test.

ods_ci/tests/Resources/Page/ODH/JupyterHub/JupyterHubSpawner.robot

@@ -174,18 +174,18 @@ Add Spawner Environment Variable
 
 Remove All Spawner Environment Variables
    [Documentation]  Removes all existing environment variables in the Spawner
-   @{env_vars_list} =    Create List
-   @{env_elements} =    Get WebElements    xpath://*[.='Variable name']/../../div[2]/input
-
-   # We need to fist get the env values and remove them later to avoid a
-   # selenium error due to modifiying the DOM while iterating its contents
-   FOR    ${element}    IN    @{env_elements}
-       ${txt} =   Get Value  ${element}
-       Append To List  ${env_vars_list}   ${txt}
-   END
-
-   FOR    ${env}    IN    @{env_vars_list}
-       Remove Spawner Environment Variable   ${env}
+   ${remove_env_btn_xpath} =    Set Variable    //*[@data-id="remove-env-var-button"]
+   ${first_remove_env_btn_xpath} =    Set Variable
+   ...    //*[@class="odh-notebook-controller__env-var-row"][1]${remove_env_btn_xpath}
+
+   WHILE    ${TRUE}
+       ${remove_btn_number} =    Get Element Count    ${remove_env_btn_xpath}
+       IF    ${remove_btn_number} > 0
+           Click Button    ${first_remove_env_btn_xpath}
+           Sleep    0.5s    # Give browser time to react
+       ELSE
+           BREAK
+       END
    END
 
 Remove Spawner Environment Variable
@@ -359,8 +359,8 @@ Spawn Notebook With Arguments  # robocop: disable
                 Capture Page Screenshot    reload.png
                 Wait Until JupyterHub Spawner Is Ready
             END
+            Remove All Spawner Environment Variables
             IF  &{envs}
-                Remove All Spawner Environment Variables
                 FOR  ${key}  ${value}  IN  &{envs}[envs]
                     Sleep  1
                     Add Spawner Environment Variable  ${key}  ${value}